This proposal is for a K01 Mentored Research Scientist Development Award for Dr. Chad Rethorst, Assistant Professor in the Department of Psychiatry at University of Texas Southwestern Medical Center. The K01 award will provide the Dr. Rethorst with the additional training and experience necessary to become an independent investigator studying the effects of physical activity on mental health. The proposed career development plan includes focused coursework, mentorship from a multi-disciplinary group of established researchers and practical research experience. The training plan focuses on two training objectives: (1) training in the design and conduct of RCTs in clinical population, (2) training in psychopathology diagnosis and assessment and (3) advanced training in biostatistical methods. Dr. Madhukar Trivedi will serve as the primary mentor and will oversee the training plan. Dr. Trivedi has extensive experience in the design and conduct of multisite trials in mood disorders. Dr. Steve Blair and Dr. Thomas Carmody will provide additional mentorship. Dr. Blair has extensive experience in conducting RCTs using exercise interventions in clinical populations. Dr. Carmody is an expert in study design and longitudinal analysis of projects in the area of mental health. The research project is a pilot study of an exercise intervention to prevent depression in Hepatitis C patients receiving Interferon-alpha (IFN- ) treatment. IFN- is an efficacious treatment for Hepatitis C (HPC); however, IFN- treatment results in a significant increase in depressive symptoms. The potential of an exercise intervention to prevent depression during IFN- treatment is supported by longitudinal data demonstrating that physical activity reduces future risk of depression. Furthermore, exercise is efficacious as a stand-alone and/or adjunctive treatment for depression. Participants will be recruited from the Clinical Center for Liver Diseases at UT-Southwestern and randomized to 26 weeks of either: aerobic exercise or a health education control group. The aims of the pilot study are: 1) to examine the feasibility of recruitment and randomization of eligible HCV patients into an RCT, 2) to examine the feasibility of maintaining participant engagement throughout the duration of the trial, 3) to conduct an analysis of the preliminary efficacy of an exercise intervention in preventing depression in Hepatitis C patients receiving IFN- treatment, and 4) to conduct an analysis of the preliminary effects of an exercise intervention on mediators of IFN- induced depression in HPC patients receiving IFN- treatment. The successful completion of the proposed research and training plan will provide the knowledge and experience necessary to progress Dr. Rethorst toward his career goal of becoming an independent investigator examining the role of physical activity in the treatment and prevention of mental illness. Specifically, the data obtained from the proposed pilot study will serve as the basis for an R01 application to be submitted during the final year of the K01 award. The R01 will propose an RCT sufficiently powered to examine the efficacy of an exercise intervention in the prevention of IFN- -induced depression.